Waking Up Early Is Making Us Fat

Illustration by Taylor Callery

Are you socially jet-lagged? If you need an alarm clock to wake up, then you probably are. The term, coined by Till Roenneberg, a chronobiologist at Ludwig-Maximilians University in Munich, refers to what happens when your internal body clock wants you to stay asleep but your external social clock wants you to wake up. By getting up with our alarms all week and sleeping late on the weekends, it's like sending our body clock to the West Coast and dragging it back East Monday morning. The result, says Roenneberg, is that "there are people who, caught in a cycle of sleep loss and oversleeping, hardly ever get a normal night's sleep at all."

The problem is that this increasingly describes most of us. If majoritarian rules applied to society, and we weren't chasing the global economy, most people would happily nod off between 12 a.m. and 1 a.m. and wake between 8 a.m. and 9 a.m. Instead, "85 percent of us need an alarm clock to wake up," says Roenneberg, with the result that "two thirds of normal people suffer from one hour or more of social jet-lag, 16 percent two hours, and shift workers considerably more."

Shift work is particularly vicious. Orfeo Buxton, a sleep researcher at Harvard University Medical School, recently led the first study in humans where sleep was disrupted for several weeks to simulate the effects of shift work. The result was metabolic chaos: glucose spiked to levels that could, over time, trigger diabetes, while energy expenditure slumped to the point where subjects would have gained up to 13 pounds in a year.

And the evidence that social jet lag might be a major factor driving obesity keeps mounting: Roenneberg's team just published an analysis of thousands of sleep records which found a 33 percent increase in obesity for every hour of social jet lag. Sleep loss, says Buxton, triggers a feedback loop that "makes people prefer processed and sugary foods over fruit and vegetables, while leaving them with less energy to exercise."

This year will be a landmark year for sleep research, both researchers say, one that frames sleeplessness as a physiological revolution that we must fight to reverse. "We need to get rid of the old rule that the early bird catches the worm," says Roenneberg. When we are wired to rise late, this is nothing but "pure stupidity."

"In the developed world," says Buxton, "we're subjecting ourselves to a giant unnatural experiment in the presence of excess food." And right now, he says, it looks as if "everyone's turning into a tub of lard."